Fuel level gauge control systems and methods

ABSTRACT

A system includes a fuel level determination module, an adjusting module, and a gauge control module. The fuel level determination module outputs a measured fuel level based on a fuel level signal generated by a fuel level sensor. After an ignition system of the vehicle is turned on, the adjusting module adjusts a present fuel level toward the measured fuel level based on a first rate when a refueling event was detected while the ignition system was off and adjusts the present fuel level toward the measured fuel level based on a second rate when a refueling event was not detected while the ignition system was off. The first rate is faster than the second rate. The gauge control module controls a fuel level gauge to display the present fuel level.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/485,343, filed on May 12, 2011. The disclosure of the aboveapplication is incorporated herein by reference in its entirety.

FIELD

The present application relates to vehicles with internal combustionengines and more particularly to fuel gauge control systems and methods.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Internal combustion engines combust a mixture of air and fuel togenerate torque. The fuel of the air/fuel mixture may be liquid fueland/or vapor fuel. A fuel system is used to supply liquid fuel and/orvapor fuel to the engine. Liquid fuel is drawn from a fuel tank. A lowpressure fuel pump may draw liquid fuel from the fuel tank. The lowpressure fuel pump may provide liquid fuel to a high pressure fuel pumpor to a fuel injector. Vapor fuel is drawn from a vapor canister of apurge system.

Generally, liquid fuel is contained within the fuel tank. In somecircumstances, the liquid fuel may vaporize and form vapor fuel. Thevapor canister stores the vapor fuel. The purge system also includes apurge valve and a vent valve (i.e., a diurnal valve). Operation of theengine causes a vacuum (low pressure relative to barometric pressure) toform within an intake manifold of the engine. Selective actuation of thepurge valve and the vent valve allows the vapor fuel to be drawn intothe intake manifold, thereby purging the vapor fuel from the vaporcanister.

SUMMARY

A system includes a fuel level determination module, an adjustingmodule, and a gauge control module. The fuel level determination moduleoutputs a measured fuel level based on a fuel level signal generated bya fuel level sensor. After an ignition system of the vehicle is turnedon, the adjusting module adjusts a present fuel level toward themeasured fuel level based on a first rate when a refueling event wasdetected while the ignition system was off and adjusts the present fuellevel toward the measured fuel level based on a second rate when arefueling event was not detected while the ignition system was off. Thefirst rate is faster than the second rate. The gauge control modulecontrols a fuel level gauge to display the present fuel level.

A method includes: outputting a measured fuel level based on a fuellevel signal generated by a fuel level sensor; after an ignition systemof the vehicle is turned on, adjusting a present fuel level toward themeasured fuel level based on a first rate when a refueling event wasdetected while the ignition system was off and adjusting the presentfuel level toward the measured fuel level based on a second rate when arefueling event was not detected while the ignition system was off; andcontrolling a fuel level gauge to display the present fuel level. Thefirst rate is faster than the second rate.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples areintended for purposes of illustration only and are not intended to limitthe scope of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of an example fuel system accordingto the present disclosure;

FIG. 2 is a functional block diagram of an example fuel level gaugecontrol system according to the present disclosure;

FIG. 3 is a flowchart depicting an example method of detecting arefueling event according to the present disclosure; and

FIG. 4 is a flowchart depicting an example method of controlling a levelof fuel displayed according to the present disclosure.

DETAILED DESCRIPTION

The following description is merely illustrative in nature and is in noway intended to limit the disclosure, its application, or uses. Forpurposes of clarity, the same reference numbers will be used in thedrawings to identify similar elements. As used herein, the phrase atleast one of A, B, and C should be construed to mean a logical (A or Bor C), using a non-exclusive logical or. It should be understood thatsteps within a method may be executed in different order withoutaltering the principles of the present disclosure.

As used herein, the term module may refer to, be part of, or include anApplication Specific Integrated Circuit (ASIC); an electronic circuit; acombinational logic circuit; a field programmable gate array (FPGA); aprocessor (shared, dedicated, or group) that executes code; othersuitable components that provide the described functionality; or acombination of some or all of the above, such as in a system-on-chip.The term module may include memory (shared, dedicated, or group) thatstores code executed by the processor.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes,and/or objects. The term shared, as used above, means that some or allcode from multiple modules may be executed using a single (shared)processor. In addition, some or all code from multiple modules may bestored by a single (shared) memory. The term group, as used above, meansthat some or all code from a single module may be executed using a groupof processors or a group of execution engines. For example, multiplecores and/or multiple threads of a processor may be considered to beexecution engines. In various implementations, execution engines may begrouped across a processor, across multiple processors, and acrossprocessors in multiple locations, such as multiple servers in a parallelprocessing arrangement. In addition, some or all code from a singlemodule may be stored using a group of memories.

The apparatuses and methods described herein may be implemented by oneor more computer programs executed by one or more processors. Thecomputer programs include processor-executable instructions that arestored on a non-transitory tangible computer readable medium. Thecomputer programs may also include stored data. Non-limiting examples ofthe non-transitory tangible computer readable medium are nonvolatilememory, magnetic storage, and optical storage.

An engine combusts an air/fuel mixture to produce drive torque for avehicle. Liquid fuel and vapor fuel are drawn from a fuel tank andselectively supplied to the engine. A fuel level sensor measures a levelof liquid fuel within the fuel tank. A fuel level gauge displays apresent level of fuel within the fuel tank.

A control module generates a present fuel level and controls the fuellevel gauge to display the present fuel level. The control moduledetermines the present fuel level based on the measured fuel level and aprevious (e.g., last) value of the present fuel level (previous fuellevel). More specifically, the control module adjusts the present fuellevel toward the measured fuel level based on a difference between themeasured fuel level and the previous fuel level.

Under some circumstances, however, the difference between the measuredfuel level and the previous fuel level may be large. For example only,the difference may be large for a period after the vehicle is parked ona hill due to movement of liquid fuel within the fuel tank. If thecontrol module adjusts the present fuel level toward the measured fuellevel at too fast a rate, the fuel level gauge may display a fuel levelthat is greater than or less than the actual fuel level because of thehill. For another example only, the difference between the measured fuellevel and the previous fuel level may also be large when a refuelingevent occurs while the vehicle is shut down.

The control module of the present disclosure detects when a refuelingevent occurs while the vehicle is shut down. When the vehicle is laterstarted, the control module determines a rate for adjusting the presentfuel level toward the measured fuel level based on whether a refuelingevent was detected while the vehicle was shut down. If a refueling eventwas detected while the vehicle was shut down, the control module adjuststhe present fuel level toward the measured fuel level based on a firstpredetermined rate. The control module adjusts the present fuel leveltoward the measured fuel level based on a second predetermined rate whena refueling event was not detected while the vehicle was shut down. Thefirst predetermined rate is faster than the second predetermined rate.

In this manner, the control module adjusts the fuel level displayed viathe fuel level gauge toward the measured fuel level at a faster ratewhen a refueling event was detected while the vehicle was shut down. Thecontrol module adjusts the fuel level displayed via the fuel level gaugetoward the measured fuel level at a slower rate when a refueling eventwas not detected while the vehicle was shut down.

Referring now to FIG. 1, a functional block diagram of an example fuelsystem 100 is presented. A vehicle includes an internal combustionengine (not shown) that generates torque. For example only, the enginemay be a gasoline-type engine, a diesel-type engine, and/or anothersuitable type of engine. The engine combusts a mixture of air and fuelwithin one or more cylinders of the engine to generate torque.

In some vehicles, torque generated by the engine may be used to propelthe vehicle. More specifically, torque output by the engine istransferred to a transmission, which may then transfer torque to one ormore wheels of the vehicle. In other vehicles, such as some types ofhybrid vehicles, torque output by the engine may not be transferred tothe transmission. Instead, torque output by the engine may be convertedinto electrical energy by, for example, a generator. The electricalenergy may be provided to one or more electric motors and/or an energystorage device. The one or more electric motors use electrical energy togenerate torque to propel the vehicle. Some hybrid vehicles may alsoreceive electrical energy from an alternating current (AC) power source,such as a standard wall outlet.

The fuel system 100 supplies fuel to an engine (not shown). The fuelincludes liquid fuel and vapor fuel. The fuel system 100 includes a fueltank 102 that contains liquid fuel. Some conditions, such as heat,vibration, and/or radiation, may cause liquid fuel within the fuel tank102 to vaporize. A canister 104 traps and stores vaporized fuel (i.e.,vapor fuel). For example only, the canister 104 may include one or moresubstances, such as a charcoal substance, which absorbs and stores vaporfuel.

Operation of the engine creates a vacuum within an intake manifold ofthe engine. A purge valve 106 and a vent valve 108 may be selectivelyoperated (e.g., opened and closed) to draw vapor fuel from the canister104 to the intake manifold for combustion. In other words, operation ofthe purge valve 106 and the vent valve 108 may be coordinated to purgevapor fuel from the canister 104. An engine control module (ECM) 110 maycontrol the operation of the purge valve 106 and the vent valve 108.

At a given time, the purge valve 106 may be in an open position or aclosed position. At the given time, the vent valve 108 may too be in anopen position or a closed position. The ECM 110 may allow ambientairflow into the canister 104 by commanding the vent valve 108 to theopen position. When the vent valve 108 is in the open position, the ECM110 may command the purge valve 106 to the open position to purge vaporfuel from the canister 104 to the intake manifold. The ECM 110 maycontrol the rate at which vapor fuel is purged from the canister 104(i.e., a purge rate) by adjusting how long the purge valve 106 is in theopen position during a period of time (i.e., a purge valve duty cycle).

Vacuum within the intake manifold draws vapor fuel from the canister 104to the intake manifold via the purge valve 106. Vapor fuel drawn fromthe canister 104 may be replaced by air at ambient (barometric) pressuredrawn through the vent valve 108. The purge rate may be based on theduty cycle of the purge valve 106 and the amount of vapor fuel withinthe canister 104.

The ECM 110 commands the vent valve 108 to the open position andcontrols the duty cycle of the purge valve 106 during operation of theengine. When the engine is shut down (e.g., at key OFF), the ECM 110commands both the purge valve 106 and the vent valve 108 to theirrespective closed positions. The purge valve 106 and the vent valve 108are maintained in their respective closed positions when the engine isOFF.

Liquid fuel may be added to the fuel tank 102 via a fuel inlet 112. Afuel cap 114 closes the fuel inlet 112 and the fuel tank 102. The fuelcap 114 and the fuel inlet 112 may be accessed via a fueling compartment116. A fuel door 118 closes the fueling compartment 116. In variousimplementations, the ambient air provided to the canister 104 throughthe vent valve 108 may be drawn from the fueling compartment 116.

A vacuum may naturally form within the fuel tank 102 after the engine isshut down. The vacuum may be attributable to heating and subsequentcooling of gas (e.g., air and/or vapor fuel) present in the fuel tank102 and/or the canister 104 after the engine is shut down. The vacuummay be referred to as engine off natural vacuum (EONV).

The ECM 110 may receive various signals. For example only, the ECM 110receives a tank pressure signal from a tank pressure sensor 126 and afuel level signal from a fuel level sensor 128. The tank pressure sensor126 measures pressure within the fuel tank 102 (i.e., a tank pressure)and generates the tank pressure signal based on the pressure. The tankpressure may be measured relative to ambient air pressure in variousimplementations. While the tank pressure sensor 126 is depicted as beinglocated within the canister 104, the tank pressure sensor 126 may belocated in another suitable location, such as within the fuel tank 102.

The fuel level sensor 128 measures an amount of liquid fuel in the fueltank 102 (i.e., a fuel level) and generates the fuel level signal basedon the amount. The fuel level may be in terms of a volume, a percentageof a maximum volume of the fuel tank 102, or another suitable measure ofthe amount of fuel in the fuel tank 102. The fuel level sensor 128 mayinclude, for example, a float, a capacitive fuel level sensor, oranother suitable type of fuel level sensor.

In various implementations, the fuel tank 102 may include two or moreindividual but connected fuel compartments. One fuel level sensor may beprovided for each of the individual fuel compartments. The fuel level tobe displayed may be determined based on the signals generated by thefuel level sensors.

An ignition module 132 may include an ignition switch or button (notshown) that can be manipulated to start and shut down the vehicle. Forease of discussion only, the ignition module 132 will be discussed asincluding an ignition switch. The ignition switch may have multiplepositions, such as an OFF position, an ON position, and a CRANKposition. The ignition switch may output an ignition signal thatindicates the ignition switch position. The ECM 110 may control theengine based on the ignition signal. For example only, the ECM 110 maystart the engine, shut down the engine, and allow the engine to run whenthe ignition signal indicates the CRANK position, the OFF position, andthe ON position, respectively.

The ECM 110 may include a display control module 150. The displaycontrol module 150 controls a fuel level gauge 154 implemented within apassenger cabin of the vehicle to display a present fuel level. Thedisplay control module 150 sets the present fuel level based on the fuellevel signal provided by the fuel level sensor 128 (measured fuellevel).

The fuel level gauge 154 may include, for example, a digital fuel gauge,an electro-mechanical fuel gauge, or another suitable type of fuel levelgauge. A digital fuel gauge may include, for example, a bar display thatdisplays discrete fuel levels between empty and full, a numeric displaythat displays, for example, a volume of fuel or a percentage betweenempty and full, or another suitable digital fuel gauge. Anelectro-mechanical fuel gauge may include, for example, a needle that ispositioned between empty and full to indicate a present fuel level oranother suitable type of electro-mechanical fuel gauge. The needle maybe positioned, for example, via an electric motor, such as a steppermotor.

When the vehicle is shut down (i.e., at key OFF), the display controlmodule 150 stores the present fuel level displayed. When the vehicle islater started (i.e., at key ON), the display control module 150 beginsadjusting the displayed fuel level toward the measured fuel level.

However, the fuel level indicated by the fuel level sensor 128 maychange while the vehicle is shut down under some circumstances. For anexample only, the fuel level indicated by the fuel level sensor 128 mayincrease when fuel is added to the fuel tank 102 while the vehicle isshut down. For another example only, the fuel level indicated by thefuel level sensor 128 may increase or decrease when the vehicle isparked on a hill. Parking the vehicle on the hill can cause the fuellevel signal to indicate that the measured fuel level within the fueltank 102 is greater than or less than an actual fuel level.

When the vehicle is started and a refueling event was detected while thevehicle was shut down, the display control module 150 adjusts thepresent fuel level toward the measured fuel level at a first rate. Thedisplay control module 150 adjusts the present fuel level toward themeasured fuel level at a second rate when the vehicle is started and arefueling event was not detected. The first filtering rate is greaterthan the second filtering rate.

In this manner, the display control module 150 adjusts the fuel leveldisplayed via the fuel level gauge 154 toward the measured fuel level ata faster rate when a refueling event was detected while the vehicle wasshut down. When a refueling event was not detected, the display controlmodule 150 adjusts the fuel level displayed toward the measured fuellevel at a slower rate to prevent an inaccurate fuel level (e.g., a fuellevel caused by the vehicle being parked on a hill) to be displayed.

Referring now to FIG. 2, a functional block diagram of an example fuellevel control system is presented. A tank pressure determination module204 may receive the tank pressure signal 208 from the tank pressuresensor 126. The tank pressure determination module 204 outputs ameasured tank pressure 212 based on the tank pressure signal 208. Forexample only, the measured tank pressure 212 may include a digitizedversion of the tank pressure signal 208. The tank pressure determinationmodule 204 may sample the tank pressure signal 208 and output themeasured tank pressure 212 at a predetermined loop rate.

A refueling detection module 216 monitors the measured tank pressure 212to detect when a refueling event occurs. In response to the ignitionsystem of the vehicle being turned off (e.g., key OFF), the refuelingdetection module 216 may store the measured tank pressure 212 as aninitial tank pressure. The ignition system of the vehicle being turnedoff may be indicated by the ignition signal 220.

A timer module 224 initializes a timer value 228 in response to theignition system of the vehicle being turned off. More specifically, thetimer module 224 resets the timer value 228 to a predetermined resetvalue (e.g., zero) and starts the timer value 228 counting in responseto the ignition system of the vehicle being turned off. The timer value228 therefore tracks the period elapsed since the ignition system of thevehicle was turned off (i.e., key OFF).

The refueling detection module 216 monitors the measured tank pressure212 for a predetermined period after the ignition system of the vehicleis turned off. More specifically, the refueling detection module 216monitors the measured tank pressure 212 while the timer value 228 isless than a predetermined value (corresponding to a predeterminedperiod). The predetermined period may be a calibrated value and may beset to, for example only, approximately 10 minutes or another suitablevalue.

The refueling detection module 216 determines whether a refueling eventoccurred based on the initial tank pressure and the measured tankpressure 212 during the predetermined period. For example only, therefueling detection module 216 may determine that a refueling eventoccurred when the measured tank pressure 212 is greater than the initialtank pressure. The refueling detection module 216 may determine that arefueling event occurred when the measured tank pressure 212 is greaterthan the initial tank pressure by at least a predetermined amount and/orfor at least a predetermined period. For example only, the predeterminedamount may be approximately 4-5 inches of water or another suitablevalue. The predetermined amount may be a calibrated value and may varyfrom vehicle to vehicle.

The refueling detection module 216 may determine a delta tank pressurebased on the measured tank pressure 212 minus the initial tank pressure.The refueling detection module 216 may determine that a refueling eventoccurred when the delta tank pressure is greater than the predeterminedamount.

Because both the vent valve 108 and the purge valve 106 are in theirrespective closed positions when the ignition system of the vehicle isoff, the fuel system 100 is closed while the ignition system of thevehicle is off. Thus, the measured tank pressure 212 (and morespecifically an increase in the measured tank pressure 212) can be usedto detect the occurrence of a refueling event. As the fuel levelmeasured using the fuel level sensor 128 may change based on road gradewhere the vehicle is parked, the detection of a refueling event can bemade independently of the fuel level signal in various implementations.

The refueling detection module 216 may indicate whether a refuelingevent occurred using a refueling indicator (e.g., signal) 232. Forexample only, the refueling detection module 216 may set the refuelingindicator 232 to an active state when a refueling event has beendetected. The refueling detection module 216 may set the refuelingindicator 232 to an inactive state when a refueling event has not beendetected.

A fuel level determination module 240 receives the fuel level signal 244from the fuel level sensor 128. The fuel level determination module 240outputs a measured fuel level 248 based on the fuel level signal 244.For example only, the measured fuel level 248 may include a digitizedversion of the fuel level signal 244. The fuel level determinationmodule 240 may sample the fuel level signal 244 and output the measuredfuel level 248 at a predetermined loop rate.

In implementations with at least one additional fuel level sensor, thefuel level determination module 240 may receive a second fuel levelsignal 250. The fuel level determination module 240 may generate themeasured fuel level 248 based on both the fuel level signal 244 and thesecond fuel level signal 250.

An adjusting module 252 sets a present fuel level 256 based on themeasured fuel level 248. A gauge control module 260 controls the fuellevel gauge 154 based on the present fuel level 256. For example only,the gauge control module 260 may control the fuel level gauge 154 suchthat the present fuel level 256 is displayed via the fuel level gauge154. The fuel level gauge 154 is visible within a passenger cabin of thevehicle.

The adjusting module 252 sets the present fuel level 256 further basedon a selected adjustment parameter 264. More specifically, the adjustingmodule 252 adjusts the present fuel level 256 toward the measured fuellevel 248 based on the selected adjustment parameter 264. The selectedadjustment parameter 264 may correspond to a maximum amount foradjusting the present fuel level 256 toward the measured fuel level 248over each predetermined period. In other words, the selected adjustmentparameter 264 may correspond to a rate at which the adjusting module 252adjusts the present fuel level 256 toward the measured fuel level 248.

The adjusting module 252 may adjust the present fuel level 256 towardthe measured fuel level 248 based on the selected adjustment parameter264 using a filter. For example only, the filter may include a linearfirst-order filter, and the selected adjustment parameter 264 may be afilter coefficient. For example only, the adjusting module 252 may setthe present fuel level 256 equal to a last value of the present fuellevel 256 plus a product of the filter coefficient and a differencebetween the last value of the present fuel level and the present valueof the measured fuel level 248. When the vehicle is started, the lastvalue of the present fuel level 256 may be the value of the present fuellevel 256 when the vehicle was shut down.

A selection module 268 sets the selected adjustment parameter 264 to oneof a first adjustment parameter and a second adjustment parameter basedon the refueling indicator 232. The first and second adjustmentparameters correspond to first and second predetermined rates,respectively, for adjusting the present fuel level 256 toward themeasured fuel level 248. The first and second predetermined rates aredifferent. For example only, as filter coefficients for the first-orderlag filter, the first adjustment parameter may be approximately 0.4 andthe second adjustment parameter may be approximately 0.0013 or othersuitable values. The first and second adjustment parameters may becalibrated values and may vary from vehicle to vehicle.

The selection module 268 sets the selected adjustment parameter 264 tothe one of the first and second adjustment parameters that allows forfaster adjustment of the present fuel level 256 toward the measured fuellevel 248 when the refueling indicator 232 is in the active state. Theselection module 268 sets the selected adjustment parameter 264 to theone of the first and second adjustment parameters that allows for sloweradjustment of the present fuel level 256 when the refueling indicator isin the inactive state.

In this manner, the adjusting module 252 adjusts the present fuel level256 toward the measured fuel level 248 at the faster rate when arefueling event is detected. When a refueling event is not detected, theadjusting module 252 adjusts the present fuel level 256 toward themeasured fuel level 248 at the slower rate. Accordingly, if the vehicleis started while parked on a hill, for example, where the measured fuellevel 248 may be different than the present fuel level 256, theadjusting module 252 only adjusts the fuel level displayed via the fuellevel gauge 154 at the slow rate.

When a refueling event is detected and the selection module 268 sets theselected adjustment parameter 264 to the first adjustment parameter, theselection module 268 may selectively later set the selected adjustmentparameter 264 to the second adjustment parameter. For example only, theselection module 268 may transition the selected adjustment parameter264 from the first adjustment parameter to the second adjustmentparameter in response to the passing of a predetermined period after thevehicle is started, when the measured fuel level 248 becomes equal tothe present fuel level 256 for at least a predetermined period, and/orwhen one or more other suitable conditions are satisfied.

Referring now to FIG. 3, a flowchart depicting an example method ofdetecting a refueling event is presented. Control may start with 304when the ignition system of the vehicle is on (i.e., key ON). At 304,control determines whether the ignition system of the vehicle hastransitioned to off (i.e., key OFF). If true, control continues with308; if false, control may remain at 304.

At 308, control may initialize the timer value 228 and store themeasured tank pressure 212 as the initial tank pressure. While notassociated with the detection of a refueling event, control also storesthe present fuel level 256 when the ignition system of the vehicle isturned off. Control updates the timer value 228 at 312 and continueswith 316. The timer value 228 therefore tracks the period elapsed sincethe ignition system of the vehicle was turned off.

At 316, control determines whether the timer value 228 is greater thanthe predetermined value. If true, control may end; if false, control maycontinue with 320. Control may determine the delta tank pressure at 320.Control may set the delta tank pressure, for example, equal to themeasured tank pressure 212 minus the initial tank pressure.

Control determines whether the delta tank pressure is greater than thepredetermined amount (pressure) at 324. In other words, controldetermines whether the measured tank pressure 212 is greater than theinitial tank pressure by at least the predetermined amount at 324. Iftrue, control detects the occurrence of a refueling event and indicatesthat a refueling event has been detected at 328, and control may end. Iffalse, control indicates that a refueling event has not been detected at332 and control may return to 312. For example only, the predeterminedamount may be approximately 4-5 inches of water or another suitablevalue.

Referring now to FIG. 4, a flowchart depicting an example method ofcontrolling the fuel level displayed via the fuel level gauge 154 ispresented. Control may begin at 404 when the ignition system of thevehicle is off (i.e., key OFF). Control may determine whether theignition system of the vehicle transitioned from off to on at 404 (i.e.,key ON). If true, control may continue with 408; if false, control mayremain at 404.

At 408, control may determine whether a refueling event was detectedwhile the vehicle was shut down. If true, control may set the selectedadjustment parameter 264 to the first adjustment parameter at 412 andcontinue with 416. If false, control may set the selected adjustmentparameter 264 to the second adjustment parameter at 420 and continuewith 416. In other words, control selects the one of the first andsecond adjustment parameters that allows the present fuel level 256 tobe adjusted toward the measured fuel level 248 at the faster rate when arefueling event was detected. Conversely, control selects the one of thefirst and second adjustment that allows the present fuel level 256 to beadjusted toward the measured fuel level 248 at the slower rate when arefueling event was not detected. The refueling indicator 232 may beused as the indicator of whether a refueling event was detected.

Control may determine the present fuel level 256 based on the measuredfuel level and the selected adjustment parameter 264 at 416. In variousimplementations, control may determine the present fuel level 256 basedon a first-order lag filter, the measured fuel level 248, a last valueof the present fuel level 256, and the selected adjustment parameter 264(the selected filter coefficient). For example only, control may set thepresent fuel level 256 equal to the last value of the present fuel level256 plus the product of the selected filter coefficient and thedifference between the last value of the present fuel level 256 and themeasured fuel level 248.

Control controls the fuel level displayed via the fuel level gauge 154based on the present fuel level 256 at 424. More specifically, controlmay control the fuel level gauge 154 to display the present fuel level256. While control is shown as ending after 424, control may insteadperform 416 and 424 at a predetermined loop rate.

The broad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent to the skilled practitioner upon astudy of the drawings, the specification, and the following claims.

What is claimed is:
 1. A method for a vehicle, comprising: outputting ameasured fuel level based on a fuel level signal generated by a fuellevel sensor; after an ignition system of the vehicle is turned on,adjusting a present fuel level toward the measured fuel level based on afirst rate when a refueling event was detected while the ignition systemwas off and adjusting the present fuel level toward the measured fuellevel based on a second rate when a refueling event was not detectedwhile the ignition system was off, wherein the first rate is faster thanthe second rate; and controlling a fuel level gauge to display thepresent fuel level.
 2. The method of claim 1 further comprising settingthe present fuel level using a filter based on the measured fuel leveland a previous value of the present fuel level.
 3. The method of claim 1further comprising setting the present fuel level using a first-orderfilter based on the measured fuel level and a previous value of thepresent fuel level.
 4. The method of claim 1 further comprising settingthe present fuel level equal to a last value of the present fuel levelplus a product of a coefficient and a difference between the measuredfuel level and the last value, wherein the coefficient corresponds toone of the first and second rates.
 5. The method of claim 1 wherein thefuel level gauge is one of a digital display and an electro-mechanicalgauge.
 6. The method of claim 1 further comprising: outputting ameasured fuel tank pressure based on a tank pressure signal generated bya fuel tank pressure sensor; and selectively detecting the refuelingevent based on the measured fuel tank pressure.
 7. The method of claim 6further comprising selectively detecting the refueling event based on afirst value of the measured fuel tank pressure stored when the ignitionsystem of the vehicle is turned off and a second value of the measuredfuel tank pressure output during a predetermined period after theignition system of the vehicle is turned off.
 8. The method of claim 7further comprising selectively detecting the refueling event when thesecond value is greater than the first value.
 9. The method of claim 7further comprising detecting the refueling event when the second valueis greater than the first value by at least a predetermined amount,wherein the predetermined amount is greater than zero.